Hach Intellical MTC30101, User Manual

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Table 1 Standard potential of reference electrode (continued)
Temperature (°C) Electrode potential in mV (E
ref
)
70 172.1
65 176.4
60 180.3
55 184.4
50 188.4
45 192.3
40 196.1
35 199.8
30 203.4
25 207.0
20 210.5
15 214.0
10 217.4
5 220.9
0 224.2
Measurement—oxidation titrations procedure:
Oxidation-reduction, or redox titrations, give a simple, reliable method to identify many
substances in a solution. A redox titration consists of adding to an unknown sample, small
increment of a titrant that converts the unknown to a different oxidation state. After each
addition of titrant, the ORP/Redox electrode develops a potential proportional to the
logarithm of the ratio of the activities of the two oxidation states.
At the inflection, or end point, the titrant has completely oxidized or reduced the unknown,
causing a sharp change in the logarithm of the ratio of the activities of the two oxidation
states. A corresponding sharp change in the potential is developed by the platinum
electrode. Often several oxidizing or reducing species can be precisely identified in the
same solution by a single titration with several inflection points.
The following directions represent a general procedure for doing a redox titration once the
sample is prepared for measurement.
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